1. Field of the Invention
This invention relates to the treatment of inflammatory bowel disease (IBD). More specifically, this invention is directed to methods for treating or preventing IBD using aryl nitrone compounds. This invention is also directed to pharmaceutical compositions containing aryl nitrone compounds which are useful for the treatment or prophylaxis of IBD.
2. State of the Art
The term inflammatory bowel disease ("IBD") describes a group of chronic inflammatory disorders of unknown causes involving the gastrointestinal tract ("GI tract"). The prevalence of IBD in the US is estimated to be about 200 per 100,000 population or approximately 500,000 people. Patients with IBD can be divided into two major groups, those with ulcerative colitis ("UC") and those with Crohn's disease ("CD").
In patients with UC, there is an inflammatory reaction primarily involving the colonic mucosa. The inflammation is typically uniform and continuous with no intervening areas of normal mucosa. Surface mucosal cells as well as crypt epithelium and submucosa are involved in an inflammatory reaction with neutrophil infiltration. Ultimately, this situation typically progresses to epithelial damage with loss of epithelial cells resulting in multiple ulcerations, fibrosis, dysplasia and longitudinal retraction of the colon.
CD differs from UC in that the inflammation extends through all layers of the intestinal wall and involves mesentery as well as lymph nodes. CD may affect any part of the alimentary canal from mouth to anus. The disease is often discontinuous, i.e., severely diseased segments of bowel are separated from apparently disease-free areas. In CD, the bowel wall also thickens which can lead to obstructions. In addition, fistulas and fissures are not uncommon.
Clinically, IBD is characterized by diverse manifestations often resulting in a chronic, unpredictable course. Bloody diarrhea and abdominal pain are often accompanied by fever and weight loss. Anemia is not uncommon, as is severe fatigue. Joint manifestations ranging from arthralgia to acute arthritis as well as abnormalities in liver function are commonly associated with IBD. Patients with IBD also have an increased risk of colon carcinomas compared to the general population. During acute "attacks" of IBD, work and other normal activity are usually impossible, and often a patient is hospitalized.
Although the cause of IBD remains unknown, several factors such as genetic, infectious and immunologic susceptibility have been implicated. IBD is much more common in Caucasians, especially those of Jewish descent. The chronic inflammatory nature of the condition has prompted an intense search for a possible infectious cause. Although agents have been found which stimulate acute inflammation, none has been found to cause the chronic inflammation associated with IBD. The hypothesis that IBD is an autoimmune disease is supported by the previously mentioned extraintestinal manifestation of IBD as joint arthritis, and the known positive response to IBD by treatment with therapeutic agents such as adrenal glucocorticoids, cyclosporine and azathioprine, which are known to suppress immune response. In addition, the GI tract, more than any other organ of the body, is continuously exposed to potential antigenic substances such as proteins from food, bacterial byproducts (LPS), etc.
Once the diagnosis has been made, typically by endoscopy, the goals of therapy are to induce and maintain a remission. The least toxic agents which patients are typically treated with are the aminosalicylates. Sulfasalazine (Azulfidine), typically administered four times a day, consists of an active molecule of aminosalicylate (5-ASA) which is linked by an azo bond to a sulfapyridine. Anaerobic bacteria in the colon split the azo bond to release active 5-ASA. However, at least 20% of patients cannot tolerate sulfapyridine because it is associated with significant side-effects such as reversible sperm abnormalities, dyspepsia or allergic reactions to the sulpha component. These side effects are reduced in patients taking olsalazine. However, neither sulfasalazine nor olsalazine are effective for the treatment of small bowel inflammation. Other formulations of 5-ASA have been developed which are released in the small intestine (e.g. mesalamine and asacol). Normally it takes 6-8 weeks for 5-ASA therapy to show full efficacy.
Patients who do not respond to 5-ASA therapy, or who have a more severe disease, are prescribed corticosteroids. However, this is a short term therapy and cannot be used as a maintenance therapy. Clinical remission is achieved with corticosteroids within 2-4 weeks, however the side effects are significant and include a Cushing goldface, facial hair, severe mood swings and sleeplessness. The response to sulfasalazine and 5-aminosalicylate preparations is poor in Crohn's disease, fair to mild in early ulcerative colitis and poor in severe ulcerative colitis. If these agents fail, powerful immunosuppressive agents such as cyclosporine, prednisone, 6-mercaptopurine or azathioprine (converted in the liver to 6-mercaptopurine) are typically tried. For Crohn's disease patients, the use of corticosteroids and other immunosuppressives must be carefully monitored because of the high risk of intra-abdominal sepsis originating in the fistulas and abscesses common in this disease. Approximately 25% of IBD patients will require surgery (colectomy) during the course of the disease.
Oxygen-derived free radicals such as HO., the superoxide anion and other reactive oxygen species such as HOCl, have emerged as a common pathway of tissue injury in a wide variety of diseases whose underlying cause is an inappropriately vigorous and sustained immune response (failure to control or down regulate response to the initial, appropriate stimulus). Examples of other diseases, in addition to IBD and arthritis, where this mechanism appear to be the operative cause are ARDS, septic shock, asthma, diabetes, multiple sclerosis, uveitis, etc. Typically, both a cytokine-mediated immune response and a nonspecific inflammatory cascade are involved in the primary inappropriate response with both responses mediated through active oxygen species (oxidative stress). The inappropriate secondary response, also mediated through oxidative stress) may involve tissue damaging oxidation by neutrophils and tissue macrophages.
Various approaches have been taken to suppress this inappropriate inflammatory response. Small molecule inhibitors of the various leukotriene, PAF and cyclooxygenase pathways have shown only limited efficacy, perhaps because blocking only one of many pathways does not provide a sufficiently large decrease in overall oxidative stress. Another approach has been the use of antibodies or cloned receptor molecules which target specific proteins in the inflammatory cascade such as IL-1, IL-6 or TNF-.alpha.. However, this approach is practical only for acute conditions, like septic shock or ARDS, where IV administration and antibody formation against the therapeutic protein is less of a concern. For a chronic condition like IBD, an orally active small molecule that is fully active when dosed once-a-day would be the preferred method of treatment.
Another approach to mitigating the oxidative stress resulting from an inflammatory response is to employ nitrone-related therapeutics (NRTs). The prototype NRT is .alpha.-phenyl-t-butyl nitrone (PBN) shown below. ##STR1##
NRTs represent a new category of therapeutics with the inherent capacity to overcome the shortcomings of other previously studied compounds. Among other properties, NRTs such as PBN are believed to trap free radicals (R.) by adding the radical to form a more unreactive nitroxyl free radical.
Nitrones were first used as analytical tools capable of reacting with highly reactive radicals to yield free radical adducts that are much less reactive. In many cases, the free radical/nitrone adduct complex is stable enough to allow in vivo isolation and quantitation using electron spin resonance (ESR). The concept of using nitrones as therapeutics in, for example, neurodegenerative diseases resulted from the observations that nitrones, such as PBN, trap reactive oxygen species and/or secondary free radicals following ischemia. The therapeutic effects of nitrones may result because the nitrones convert highly reactive radicals into much less reactive products. Certain NRTs have been shown to protect experimental animals from ischemia/reperfusion injury (stroke). NRTs, administered chronically, reverse the age-associated increase in oxidatively damaged protein and the age-associated decrease in the activity of the oxidative-sensitive enzyme, glutamine synthetase, in the brain.
Accompanying the NRT-mediated changes in oxidized protein and glutamine synthetase activity is a significant improvement in the performance of animals in behavioral tests measuring short-term spatial memory. For example, it has been shown that prototype NRTs mitigate the effects of this inflammatory cascade in a number of in vivo models. Of particular interest is the consistent and well documented protection shown by PBN against the lethality induced by LPS in various rodent models of septic shock. Remarkably, PBN has also been shown to increase the life span of senescence-accelerated mice by one third, perhaps by mitigating free radical damage. PBN has also been shown to block inducible nitric oxide synthetase ("iNOS"), the enzyme responsible for producing large amounts of the highly damaging NO. Thus, PBN can both trap HO. and suppress formation of NO., potentially neutralizing the effects of the two agents considered to be the most damaging to tissue.
When evaluating the prospects of using an antioxidant to successfully treat IBD, it is perhaps also useful to consider that the anti-oxidant defense of the human colon is relatively deficient compared to human liver (mucosal levels of SOD, catalase and GSH representing 8%, 4% and 40%, respectively of liver levels), thus leaving the colon particularly sensitive to oxidative stress. A considerable number of chemical modifications have been made to increase NRTs suitability as therapeutic agents. The effects of intrinsic chemical reactivity and radical trapping ability have been examined by substituting the phenyl ring with electron donating or electron withdrawing substituents. More water soluble analogues have also been made which, for example, have a carboxylate or sodium sulfonate group on the phenyl ring. In addition, lipophilic analogues have been made with functional group substitutions on either the phenyl ring or the nitronyl nitrogen. The alkyl nitrogen substituent has also been varied through the standard straight chain and branched C.sub.3 -C.sub.5 substituents. Nitrone isosteres and related compounds have also targeted and examined for efficacy. This approach has led to various classes of compounds, such as substituted ureas, amides, thioamides, azoxy derivatives, sulphones, and hydroxamic acids. Among these, some benzamide compounds substantially similar in structure to some nitrones, such as PBN, have been shown to have activity in the treatment of Parkinson's disease, HIV dementia, and related conditions.
As a final aspect of background, in evaluating the effectiveness of compounds in the treatment of IBD, an in vivo model based upon trinitrobenzene sulfonic acid ("TNBS") is used.
References relating to the above-mentioned subjects include:
Glickman, R M (1994) Inflammatory Bowel Disease in Harrison's Principles of Internal Medicine (McGraw Hill, New York, N.Y.) Chapter 255: 1403-1416. PA1 Calkins, B M, Mendeloff, A l (1986) Epidemiology of Inflammatory Bowel Disease, Epidemiology Review 8: 60-90. PA1 Levin, B. (1992) Inflammatory Bowel Disease and Colon Cancer, Cancer (Supplement), 70: 1313-1316. PA1 Crotty, B. (1994) Ulcerative Colitis and Xenobiotic Metabolism, Lancet, 343: 35-38. PA1 Hanauer, S B, Baert, F. (1994) Medical Therapy of Inflammatory Bowel Disease, Med Clin North Am, 78: 1413-1426. PA1 MacDermott, R P (1994) Alterations in the Mucosal System in Ulcerative Colitis and Crohn's Disease, Med Clin North Am, 78: 1207-1231. PA1 Hanauer, B. (1993) Medical Therapy of Ulcerative Colitis, Lancet, 342: 412-417. PA1 Winrow, V R, Winyard, P G, Morris, C J, Blake, D R (1993) Free radicals in Inflammation: Second Messengers and Mediators of Tissue Destruction, Br Med Bull 49: 506-522. PA1 Floyd, R A and Carney, J., Nitrone Radical Traps (NRTs) Protect in Experimental Neurodegenerative Diseases, in Neuroprotective Approaches to the Treatment of Parkinson's Disease and Other Neurodegenerative Disorders (Olanow, C W, Jenner, P and Youssim E, Eds.) Academic Press, New York, N.Y., in press. PA1 Cao, X. and Phillis, J W (1994) a-Phenyl-N-tert-butyl-nitrone Reduces Cortical Infarct and Edema in Rats Subjected to Focal Ischemia. Brain Res. 644: 267-272. PA1 Zhao, Q., Pahlmark, K., Smith, M.-J., and Siesjo, B. (1994) Delayed Treatment with the Spin Trap a-phenyl-n-tert-butyl nitrone (PBN) Reduces Infarct Size Following Transient Middle Cerebral Artery Occlusion in Rats. Acta Physiol. Scad. 152: 349-350. PA1 Oliver, C N, Starke-Reed, P E, Stadtman, E R, Carney, J M and Floyd, R A (1990) Oxidative Damage to Brain Proteins, Los of Glutamine Synthetase Activity and Production of Free Radicals During Ischemia Induced Injury to Gerbil Brain. Proc. Natl. Acad. Sci. USA 87: 5144-5147. PA1 Carney, J M, Starke-Reed, P E Oliver, C N, Landrum, R W, Cheng, M S, Wu, J F and Floyd, R A (1991) Reversal or age-related increase in brain protein oxidation in enzyme activity, and loss in temporal and spatial memory by chronic administration of the spin-trapping compound N-tert-butyl-.alpha.-phenylnitrone. Proc. Natl. Acad. Sci., 88: 3633-3636. PA1 Novelli, G P (1992) Oxygen Radicals in Experimental Shock: Effects of Spin-Trapping Nitrones in Ameliorating Shock Pathophysiology, Critical Care Medicine, 20: 499-507. PA1 Hamburger, S A, McCay, P B (1989) Endotoxin-Induced Mortality in Rats is Reduced by Nitrones, Circulatory Shock, 29: 329-334. PA1 Progrebniak, H W, Merino, M J, Hahn, S M, Mitchell, J B, Pass, H I (1992) Spin Trap Salvage from Endotoxemia: The Role of Cytokine Down-Regulation, Surgery, 112: 130-139. PA1 McKechnie, K., Furman, B L, Paratt J R (1986), Modification by Oxygen Free Radical Scavengers of the Metabolic and Cardiovascular Effects of Endotoxin Infusion in Conscious Rats, Circulatory Shock 19: 429-439. PA1 Edamatsu,R, Mori,A., Packer, L (1995) The Spin Trap N-tert-.alpha.-phenyl-butylnitrone Prolongs the Life Span of the Senescence Accelerated Mouse, Biochem Biophys Res Comm 211: 847-849. PA1 Miyajima, T., Kotake, Y. (1995) Spin Trapping Agent, Phenyl N-Tert_Butyl Nitrone, Inhibits Induction of Nitric Oxide Synthase in Endotoxin-Induced Shock in Mice, Biochem Biophys Res Commun, 215: 114-121. PA1 Boettner, G R (1987) ESR Parameters of Spin Adducts, Free Radical Biology, 3: 259-303. PA1 Harris, M L, Schiller, H J, Reilly, P M, Donowitz, M, Grisham, M B, Bulkley (1992), Free Radicals and Other Reactive Oxygen Metabolites in Imflammatory Bowel Disease: Cause, Consequence or Epiphenomenom, Pharmacol. Ther., 53: 375-408. PA1 Grisham M B, MacDermott, R P, Deitch E A (1990), Oxidant Defence Mechanisms in the Human Colon, Inflammation, 14: 669-680. PA1 Elson, C O, Startor, R B, Tennyson, G S, Ridell, R H (1995), Experimental Models of Inflammatory Bowel Disease, Gastroenterology, 109: 1344-1367. PA1 Yamada, T, Marshall, S, Specian, R D, Grisham, M B (1992) A Comparative Analysis of Two Models of Colitis in Rats, Gastroenterology, 102: 1524-1534. PA1 Wallace, J A, MacNaughton, W K, Morris, G P, Beck P L (1989) Inhibition of Leulotriene Synthesis Markedly Accelerates Healing in a Rat Model of Inflammatory Bowel Disease, Gastroenterology, 95: 29-35. PA1 Higa, A. McKnight, G W, Wallace, J L (1993) Attenuation of Epithelial Injury in Acute Experimental Colitis by Immunomodulators, Eur. J. Pharmacol. 239: 171-178. PA1 Castro, G A, Roy, S A, Stockstill, R D (1974) Trichinella Spiralis: Peroxidase Activity in Isolated Cells from the Rat Intestine, Exp. Parasitol., 36: 307-315. PA1 N-cyclohexyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-tert-butyl-.alpha.-(3,5-di-tert-butyl-2-hydroxyphenyl)nitrone, PA1 N-isobutyl-.alpha.-phenylnitrone, PA1 N-tert-butyl-.alpha.-(4-benzyloxyphenyl)nitrone, PA1 N-cyclobutyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-benzyl-.alpha.-(4-acetamidophenyl)nitrone, PA1 N-cyclopentyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-tert-butyl-.alpha.-(1-methylindol-3-yl)nitrone, PA1 N-tert-butyl-.alpha.-(3,5-di-tert-butyl-4-acetoxy)nitrone, PA1 spiro[cyclohexane-1,3']-6-methoxy-3,4-dihydroisoquinoline-N-oxide, PA1 N-tert-butyl-.alpha.-(4-aminosulfonylphenyl)nitrone, PA1 and pharmaceutically acceptable salts thereof. PA1 N-cyclohexyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-tert-butyl-.alpha.-(3,5-di-tert-butyl-2-hydroxyphenyl)nitrone, PA1 N-isobutyl-.alpha.-phenylnitrone, PA1 N-tert-butyl-.alpha.-(4-benzyloxyphenyl)nitrone, PA1 N-cyclobutyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-benzyl-.alpha.-(4-acetamidophenyl)nitrone, PA1 N-cyclopentyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-tert-butyl-.alpha.-(1-methylindol-3-yl)nitrone, PA1 N-tert-butyl-.alpha.-(3,5-di-tert-butyl-4-acetoxy)nitrone, PA1 spiro[cyclohexane-1,3']-6-methoxy-3,4-dihydroisoquinoline-N-oxide, PA1 N-tert-butyl-.alpha.-(4-aminosulfonylphenyl)nitrone, PA1 and pharmaceutically acceptable salts thereof. PA1 (a) identifying a patient suffering from or susceptible to an inflammatory bowel condition; and PA1 (b) administering to said patient a pharmaceutical composition comprising a pharmaceutically acceptable carrier and an effective inflammatory bowel condition-treating amount of a compound selected from the group consisting of: PA1 N-cyclohexyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-tert-butyl-.alpha.-(3,5-di-tert-butyl -2-hydroxyphenyl)nitrone, PA1 N-isobutyl-.alpha.-phenylnitrone, PA1 N-tert-butyl-.alpha.-(4-benzyloxyphenyl)nitrone, PA1 N-cyclobutyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-benzyl-.alpha.-(4-acetamidophenyl)nitrone, PA1 N-cyclopentyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-tert-butyl-.alpha.-(1-methylindol-3-yl)nitrone, PA1 N-tert-butyl-.alpha.-(3,5-di-tert-butyl-4-acetoxy)nitrone, PA1 spiro[cyclohexane-1,3 ']-6-methoxy-3,4-dihydroisoquinoline-N-oxide, PA1 N-tert-butyl-.alpha.-(4-aminosulfonylphenyl)nitrone, PA1 and pharmaceutically acceptable salts thereof. PA1 N-isobutyl-.alpha.-phenylnitrone, PA1 N-cyclobutyl-.alpha.-(2-ethoxyphenyl)nitrone, PA1 N-benzyl-.alpha.-(4-acetamidophenyl)nitrone, PA1 N-tert-butyl-.alpha.-(1-methylindol-3-yl) nitrone, PA1 N-tert-butyl-.alpha.-(4-aminosulfonylphenyl)nitrone, PA1 and pharmaceutically acceptable salts thereof.